1. Field of the Invention
The present invention relates to an image reader and an image forming apparatus for use in a digital copier, a scanner, a facsimile, or the like.
2. Description of the Related Art
Under recent conditions where importance is placed on environmental protection and energy conservation, efforts are continuously made to design copiers, multifunction peripherals (MFPs), and the like to meet criteria of Energy Star (registered trademark), ZESM, or the like that are proposed with the aim of saving energy. These criteria are designed to save energy and set a limit on energy consumption of equipment in a standby state (a state into which the equipment is put when the equipment remains unused for a predetermined period of time after power-on of a main power supply, and in which power supply to a portion of the equipment is stopped and the equipment waits for a return instruction).
In a conventional power save mode in a standby state employed by a typical copier or MFP, power supply to large-power-consuming components such as a fixing heater and an operation panel are switched off or switched to low-power operation, and power supply to a scanner is entirely switched off.
When the copier or the MFP that is in the standby state is used, a user needs to wait until power supply is turned on so that the copier or the MFP return from a low-power operation state to a normal operation state to bring the copier or the MFP to a state where the copier or the MFP can be used. This waiting time is felt by the user to be longer than its actual length, and stresses the user.
More specifically, at a time of returning from the standby state, a scanner section performs the following adjustment, or control when power supply is switched on so that an obtained analog image signal is converted into a digital image signal accurately.                Adjustment of an amplification factor to increase the analog image signal to an appropriate level        Adjustment of a reference level for optimization of a black level        
Accordingly, in a case where power supply to a scanner section is to be stopped in the standby state, a conventional process of returning from the standby state disadvantageously requires time to perform the adjustment or control described above, causing the user to wait longer.
Under these circumstances, there have conventionally been proposed techniques including a technique of reducing time required to perform the adjustment or control operations described above by not performing initialization of a traveling member (detection of a home position of the traveling member) that would otherwise be performed before gain control (Japanese Patent Application Laid-open No. 2002-118726) and a technique of reducing time required to perform the adjustment or control described above by using a value having been stored before entering the power save mode, as an initial control value of the adjustment or control described above (Japanese Patent Application Laid-open No. 2002-112027 and Japanese Patent Application Laid-open No. 2002-077520).
However, in recent years, in addition to reduction in return time achieved by techniques as disclosed in Japanese Patent Application Laid-open No. 2002-118726, 2002-112027, or 2002-077520, further reduction in return time is necessitated.
There is a need to further reduce waiting time until it becomes possible to perform scan from when being in a power save mode while suppressing an increase in cost.